1. Field of the Invention
The present invention relates generally to pneumatic accumulators and specifically to pneumatic accumulators suitable for use on missile systems which employ heat exchangers.
2. Background of the Invention
An existing air-to-ground missile system utilizes a gaseous nitrogen accumulator as a source of pneumatic working fluid for pressurizing its guidance-vane actuators. There is now interest in developing an extended range version of the system which would offer improved flight time and endurance. These improvements will require the development of a new accumulator which can provide pneumatic fluid at acceptable pressures and temperatures for greater periods of time than that provided by the original gaseous nitrogen accumulator. Additionally, these requirements must be met without adding significant weight to the missile system while also minimizing size and complication of the accumulator. Moreover, any prospective accumulator must supply the working fluid at a temperature lower than that which will damage the plastic components of the actuators (about 400.degree. F.). The gaseous nitrogen accumulator has proven unsuitable for the newer version of the missile because its duration could be extended only by making it unacceptably large and heavy. The gaseous nitrogen accumulator also suffers the disadvantage that the temperature of the contained nitrogen falls off rapidly as nitrogen gas is discharged therefrom, which effect shortens duration, reduces the volumetric flow rate and causes a significant amount of residual nitrogen to remain unused within the system.
With respect to the problem of residual gas, the prior practice has been to provide the storage tank of gaseous accumulator systems with internal heat exchangers through which a heated, secondary fluid is circulated. The heat extracted from the secondary fluid serves to allay the drop in temperature resulting from the rapid discharge of fluid from the storage tank. However, these systems require a second storage tank for containing a supply of the secondary fluid and also means for heating the secondary fluid. The latter element usually comprises ducting leading through a section of the rocket combustor and/or thrust chamber and in other arrangements, might comprise a gas generator. Any of these arrangements adds significant complication and weight to the overall missile system, and the ducting through the storage tank itself creates further problems in regard to sealing the entrance and the exit of the ducts through the primary storage tank. Moreover, in many prior art arrangements, significant danger of explosion arises if the secondary fluid and the contained fluid were ever to mix and thus, such systems present a cognizable risk of catastrophic engine failure.